Re: [PATCH 2/7] rust: kunit: support checked `-> Result`s in KUnit `#[test]`s

David Gow
2025-05-05T06:02:23Z

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On Sat, 3 May 2025 at 05:51, Miguel Ojeda <ojeda@kernel.org> wrote:
>
> Currently, return values of KUnit `#[test]` functions are ignored.
>
> Thus introduce support for `-> Result` functions by checking their
> returned values.
>
> At the same time, require that test functions return `()` or `Result<T,
> E>`, which should avoid mistakes, especially with non-`#[must_use]`
> types. Other types can be supported in the future if needed.
>
> With this, a failing test like:
>
> #[test]
> fn my_test() -> Result {
> f()?;
> Ok(())
> }
>
> will output:
>
> [ 3.744214] KTAP version 1
> [ 3.744287] # Subtest: my_test_suite
> [ 3.744378] # speed: normal
> [ 3.744399] 1..1
> [ 3.745817] # my_test: ASSERTION FAILED at rust/kernel/lib.rs:321
> [ 3.745817] Expected is_test_result_ok(my_test()) to be true, but is false
> [ 3.747152] # my_test.speed: normal
> [ 3.747199] not ok 1 my_test
> [ 3.747345] not ok 4 my_test_suite
>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---

This is a neat idea. I think a lot of tests will still want to go with
the () return value, but having both as an option seems like a good
idea to me.

Reviewed-by: David Gow <davidgow@google.com>

Cheers,
-- David

> rust/kernel/kunit.rs | 25 +++++++++++++++++++++++++
> rust/macros/kunit.rs | 3 ++-
> 2 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
> index 2659895d4c5d..f43e3ed460c2 100644
> --- a/rust/kernel/kunit.rs
> +++ b/rust/kernel/kunit.rs
> @@ -164,6 +164,31 @@ macro_rules! kunit_assert_eq {
> }};
> }
>
> +trait TestResult {
> + fn is_test_result_ok(&self) -> bool;
> +}
> +
> +impl TestResult for () {
> + fn is_test_result_ok(&self) -> bool {
> + true
> + }
> +}
> +
> +impl<T, E> TestResult for Result<T, E> {
> + fn is_test_result_ok(&self) -> bool {
> + self.is_ok()
> + }
> +}
> +
> +/// Returns whether a test result is to be considered OK.
> +///
> +/// This will be `assert!`ed from the generated tests.
> +#[doc(hidden)]
> +#[expect(private_bounds)]
> +pub fn is_test_result_ok(t: impl TestResult) -> bool {
> + t.is_test_result_ok()
> +}
> +
> /// Represents an individual test case.
> ///
> /// The [`kunit_unsafe_test_suite!`] macro expects a NULL-terminated list of valid test cases.
> diff --git a/rust/macros/kunit.rs b/rust/macros/kunit.rs
> index eb4f2afdbe43..9681775d160a 100644
> --- a/rust/macros/kunit.rs
> +++ b/rust/macros/kunit.rs
> @@ -105,8 +105,9 @@ pub(crate) fn kunit_tests(attr: TokenStream, ts: TokenStream) -> TokenStream {
> let path = crate::helpers::file();
> for test in &tests {
> let kunit_wrapper_fn_name = format!("kunit_rust_wrapper_{}", test);
> + // An extra `use` is used here to reduce the length of the message.
> let kunit_wrapper = format!(
> - "unsafe extern \"C\" fn {}(_test: *mut kernel::bindings::kunit) {{ {}(); }}",
> + "unsafe extern \"C\" fn {}(_test: *mut kernel::bindings::kunit) {{ use kernel::kunit::is_test_result_ok; assert!(is_test_result_ok({}())); }}",
> kunit_wrapper_fn_name, test
> );
> writeln!(kunit_macros, "{kunit_wrapper}").unwrap();
> --
> 2.49.0
>

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